6 ms·
https://www.grc.nasa.gov/www/k-12/airplane/move.html https://www.grc.nasa.gov/www/k-12/airplane/move.html ground speed is the speed of the plane, relative to a
by ozzyman700 8y ago
https://www.grc.nasa.gov/www/k-12/airplane/move.html https://www.grc.nasa.gov/www/k-12/airplane/move.html
ground speed is the speed of the plane, relative to an observer on the ground, air speed is how fast the people on the plane are going relative to themselves.
Airspeed = Ground Speed - Wind Speed (wind blowing towards front of plan is positive, tailwind is negative)
- BonesJustice 8y agoI’m a bit under the weather, so my comprehension may be lacking, but I think you’ve got your signs reversed (or your head/tail terminology flipped). If tail wind (moving with the plane) were negative, then air speed would exceed ground speed. Intuitively, that doesn’t make sense. Air speed can only exceed ground speed if the wind is blowing in an opposing direction, i.e., the plane must travel faster against the wind to achieve the same speed relative to a ground observer.
- deleted 8y ago[deleted]
- FabHK 8y agoWind is "named" after where it comes from. If you fly north, and the wind is a north wind, you fly slower. (This terminology is in line with what GP said.) Then, ground speed = air speed - wind speed. Thus, GP seems to have either the sign wrong, or ground and air speed mixed up (but not both :-)
- bartread 8y ago> Wind is "named" after where it comes from. This is absolutely true, but has always infuriated me because it seems needlessly contrary as compared to the way we speak about anything else travelling in a direction as read from a compass. Does anybody know why it's the case?
- ahartmetz 8y agoProbably because it matters where the air was before. Stuff like: north wind is could, south wind is warm, west wind is humid, etc
- bartread 8y agoDoesn't that very much depend on where you are though? E.g., with respect to the equator, major bodies of water and landmasses, mountain ranges, prevailing weather conditions. Also perhaps on seasons. I can understand that it might be just an ancient tradition originating from a particular part of the world, that we've turned into a convention, but it loses meaning when you go elsewhere.
- Arnt 8y agoIt rather depends on where you are, but so does language. The words we use were cast locally. If you speak English some words were cast in the Ukraine, some in Germany, some in Rome, some in France, some in Britain, but the people living in those places weren't obliged to make the words globally meaningful. If you go to Cape Town, a "north wind" presumably doesn't mean cold, because the area north of the city isn't colder than the city itself. This didn't matter to the people who first said "north wind" and I don't think it means much nowadays either. Just another little thing to watch out for in intercultural communication.
- yesenadam 8y agoCan you name anything else named after where it's going, not where it comes from? I can't think of anything named like that, but I guess there must be some.
- subhro 8y agoNo you are right. In case of tailwind, it is KIAS + WS whereas headwind is KIAS - WS KIAS: Knots Indicated Airspeed (i.e. the speed at which air is hitting the pitot tube) WS: Wind speed
- aeijdenberg 8y agoSlight, but important (if you don't want to run out of fuel) nit, indicated airspeed (KIAS) is not the same as true airspeed (KTAS). To calculate ground speed (as required for navigation and fuel planning) you need true airspeed (not indicated) as well as wind direction and speed. See some discussion here: https://www.quora.com/In-aviation-what-is-the-difference-between-IAS-CAS-EAS-and-TAS https://www.quora.com/In-aviation-what-is-the-difference-bet...
- TylerE 8y agoNot so slight. At airliner altitudes they can differ by 50% or so. IAS is what the pilots care about while flying because it’s what matters for aerodynamics (ie stall speed)
- ars 8y ago> are going relative to themselves. You mean relative to the air outside the window. Relative your yourself you're always standing still.
- stephenr 8y agoMost people on the plane were probably sitting still. I'll show myself out.
- cmurf 8y agoFor a given altitude, trim, and power, the airspeed is always the same no matter the wind. Wind only affects groundspeed. Ground speed = true airspeed + wind component (where you're computing a vector based on wind direction to determine what amount of it is either tail wind (+) or headwind (-).
- robotresearcher 8y ago> For a given altitude, trim, and power, the airspeed is always the same no matter the wind. If acceleration is zero. (Internet, therefore pedantry).
- Bendingo 8y ago> air speed is how fast the people on the plane are going relative to themselves That makes no sense. How can people be moving relative to themselves?
- jazzyjackson 8y agorelative to their own location Δt ago?
- cxseven 8y agoLocation with respect to what?
- FPGAhacker 8y agoThemselves meaning the ground observer as that was the point of view GP was speaking about.